MEMS structure and method of forming same

Abstract

A microelectromechanical system (MEMS) device includes a substrate and a movable element at least partially suspended above the substrate and having at least one degree of freedom. The MEMS device further includes a protrusion extending from the substrate and configured to contact the movable element when the movable element moves in the at least one degree of freedom, wherein the protrusion comprises a surface having a water contact angle of higher than about 15° measured in air.

What is claimed is: 
     
       1. A method of forming a MEMS device, the method comprising:
 forming a plurality of interconnect layers embedded in a respective plurality of stacked dielectric layers on a first substrate; 
 forming a top dielectric layer over the plurality of interconnect layers; 
 etching into the top dielectric layer a first cavity having a first floor and a second cavity having a second floor; 
 forming on the first floor a protrusion having a low surface energy relative to the surface energy of the top dielectric layer; 
 forming a MEMS wafer over the top dielectric layer, the MEMS wafer having a movable element at least partially suspended above the first cavity, wherein the protrusion is in a path of movement of the movable element when the movable element is deflected in a first direction; 
 etching a via extending through the MEMS wafer, the via being aligned with the second cavity; and 
 forming a conductor in the via and the second cavity to electrically couple an element of the MEMS wafer to an element on the second floor of the second cavity. 
 
     
     
       2. The method of  claim 1 , wherein the forming on the first floor the protrusion comprises:
 patterning the first floor of the first cavity to form a protrusion extending therefrom; 
 forming a conductive film over the patterned first floor of the first cavity, the conductive film having the low surface energy relative to the surface energy of the top dielectric layer; and 
 removing the conductive film from at least a portion of the first floor of the first cavity while leaving the conductive film overlying the protrusion. 
 
     
     
       3. The method of  claim 1 , wherein the forming on the first floor the protrusion comprises forming a metal feature on the first floor. 
     
     
       4. The method of  claim 1 , wherein the MEMS wafer comprises a silicon surface and the top dielectric layer comprises a silicon oxide surface, and wherein the forming the MEMS wafer over the top dielectric layer comprises bringing the silicon surface and the silicon oxide surface into contact. 
     
     
       5. The method of  claim 1 , further comprising forming an electrical path between the protrusion and a voltage potential node. 
     
     
       6. The method of  claim 5 , wherein the forming the electrical path between the protrusion and the voltage potential node comprises electrically coupling the protrusion to at least one of a ground potential, a voltage potential, or a potential of the movable element. 
     
     
       7. A method of forming a MEMS device, the method comprising:
 etching a first cavity and a second cavity in a topmost dielectric layer of a substrate, the first cavity laterally separated from the second cavity, the substrate further comprising a plurality of stacked dielectric layers beneath the topmost dielectric layer, the plurality of stacked dielectric layers having a plurality of interconnect layers formed therein; 
 forming a protrusion extending from a floor of the first cavity; 
 bonding a MEMS wafer to the top dielectric layer; 
 patterning the MEMS wafer to form a movable element at least partially suspended above the first cavity, wherein the protrusion is in a path of movement of the movable element when the movable element is deflected in a first direction; 
 etching a via through the MEMS wafer, the via aligned with the second cavity; and 
 at least partially filling the via and the second cavity with a conductive material, the conductive material electrically coupling an element on the MEMS wafer to at least one of the plurality of interconnect layers of the substrate. 
 
     
     
       8. The method of  claim 7 , wherein the etching the first cavity and the second cavity in the topmost dielectric layer of the substrate exposes a portion of an interconnect layer of the plurality of interconnect layers. 
     
     
       9. The method of  claim 7 , wherein forming the protrusion extending from the floor of the first cavity comprises patterning the topmost dielectric layer to leave portions thereof remaining in the first cavity, and lining the protrusion with a conductive layer. 
     
     
       10. The method of  claim 9 , wherein the conductive layer comprises a surface having a water contact angle of higher than about 15° measured in air. 
     
     
       11. The method of  claim 7 , further comprising electrically connecting the protrusion and an interconnect layer of the plurality of interconnect layers. 
     
     
       12. A method of forming a MEMS device, the method comprising:
 forming a plurality of interconnect layers embedded in a respective plurality of stacked dielectric layers on a first substrate; 
 forming a silicon oxide layer over the plurality of interconnect layers; 
 etching into the silicon oxide layer a first cavity having a first floor and a second cavity having a second floor; 
 forming on the first floor a protrusion having a water contact angle of higher than about 15° measured in air; 
 forming a MEMS wafer over the silicon oxide layer, the MEMS wafer having a movable element at least partially suspended above the first cavity, wherein the protrusion is in a path of movement of the movable element when the movable element is deflected in a first direction; 
 etching a via extending through the MEMS wafer, the via being aligned with the second cavity; and 
 forming a conductor in the via and the second cavity to electrically couple an element of the MEMS wafer to an element on the second floor of the second cavity. 
 
     
     
       13. The method of  claim 12 , wherein the forming on the first floor the protrusion comprises:
 patterning the first floor of the first cavity to form a protrusion extending therefrom; 
 forming a conductive film over the patterned first floor of the first cavity, the conductive film having a low surface energy relative to the surface energy of the silicon oxide layer; and 
 removing the conductive film from at least a portion of the first floor of the first cavity while leaving the conductive film overlying the protrusion. 
 
     
     
       14. The method of  claim 13 , wherein the conductive film includes comprises TiN. 
     
     
       15. The method of  claim 12 , wherein the forming on the first floor the protrusion comprises forming a metal feature on the first floor. 
     
     
       16. The method of  claim 12 , wherein the MEMS wafer comprises a silicon surface, and wherein the forming the MEMS wafer over the silicon oxide layer comprises bringing the silicon surface and the silicon oxide layer into contact. 
     
     
       17. The method of  claim 12 , further comprising forming an electrical path between the protrusion and a voltage potential node. 
     
     
       18. The method of  claim 17 , wherein the forming the electrical path between the protrusion and the voltage potential node comprises electrically coupling the protrusion to at least one of a ground potential, a voltage potential, or a potential of the movable element. 
     
     
       19. The method of  claim 12 , further comprising electrically coupling the protrusion to a potential voltage node. 
     
     
       20. The method of  claim 12 , further comprising electrically coupling the protrusion to a ground node or a power supply voltage node.